Gr. okutokos, from oxus = sharp, swift and tokos = childbirth.

Oxytocin was discovered in 1909 when Sir Henry H. Dale found that an extract from the human posterior pituitary gland contracted the uterus of a pregnant cat. (The hormone is found unchanged in every mammalian species.) Dale named the unknown substance oxytocin, using the Greek words for “quick” and “birth.” As early as 1911, physicians began using the pituitary extract to stimulate childbirth contractions. Dale subsequently found that the same extract facilitates the release of mother’s milk. Oxytocin contracts the smooth-muscle cells surrounding the mammary glands to move milk into the nipple–called milk “let-down.” Source

Oxytocin‘s molecular structure was determined in 1952.[14] In the early 1950s, American biochemist Vincent du Vigneaud found that oxytocin is made up of nine amino acids, and he identified its amino acid sequence, the first polypeptide hormone to be sequenced.[15] In 1953, du Vigneaud carried out the synthesis of oxytocin, the first polypeptide hormone to be synthesized.[16][17][18] Du Vigneaud was awarded the Nobel Prize in 1955 for his work.[19]

Further work on different synthetic routes for oxytocin, as well as the preparation of analogues of the hormone (e.g. 4-deamido-oxytocin) was performed in the following decade by Iphigenia Photaki.[20]